Japan won over scores of poorer nations with a campaign that played on fears that a ban would devastate their economies. Tokyo also raised doubts that such a radical move was scientifically sound.

In another blow to conservationists, a proposal at the meeting to ban the international sale of polar bear skins failed to pass.

With stocks of Atlantic bluefin tuna down 75% due to the rapacious appetites of Japanese sushi lovers, the defeat of the proposal was a stunning setback for the Americans, Europeans and their conservationist allies who had hoped the 175-nation Convention on International Trade in Endangered Species, or CITES, would protect the fish.

"Let's take science and throw it out the door," Susan Lieberman, director of international policy with the Pew Environment Group in Washington, said sarcastically.

"It's pretty irresponsible of the governments to hear the science and ignore the science," she said. "Clearly, there was pressure from the fishing interests. The fish is too valuable for its own good."

Japan, which imports 80% of the tuna, had lobbied delegates hard to kill the proposal. They even held a reception Wednesday night for uncertain delegates that included plenty of bluefin sushi.

When Monaco introduced its proposal Thursday, the gallery was filled with critics who ignored a plea to save the once-abundant species that roams across vast stretches of the Atlantic Ocean and grows as big as 1,500 pounds.

There is an increasing demand for raw tuna for traditional dishes such as sushi and sashimi. The bluefin variety -- called "hon-maguro" in Japan -- is particularly prized, with a 440-pound Pacific bluefin tuna fetching a record 20.2 million yen ($220,000) last year.

"This exploitation is no longer exploitation by traditional fishing people to meet regional needs," Monaco's Patrick Van Klaveren told delegates. "Industrial fishing of species is having a severe effect on numbers of this species and its capacity to recover. We are facing a real ecosystem collapse."

But it became clear that the proposal had little support. Only the United States, Norway and Kenya supported the proposal outright. The European Union asked that its implementation be delayed until May 2011 to give authorities time to respond to concerns about overfishing.

Fishing nations from Africa, Asia, Latin America and the Caribbean complained that any ban would damage their fishing communities and that fears of the stock's collapse were overstated. Libya, in a rambling defense of its position, went so far as to accuse Monaco of lying and trying to mislead delegates before calling for the vote.

Under CITES rules, a country can attempt to bring a proposal back to a vote, but Monaco said it wouldn't.

Japan acknowledged the stocks were in trouble but echoed a growing consensus at the meeting that CITES should have no role in regulating tuna and other marine species. It expressed a willingness to accept lower quotas for bluefin tuna but wanted those to come from the International Commission for the Conservation of Atlantic Tunas, or ICCAT, which currently regulates the trade.

"Japan is very much concerned about the status of Atlantic bluefin tuna and Japan has been working so hard for many years to ensure recovery," Masanori Miyahara, chief counselor of the Fisheries Agency of Japan, told delegates. "But our position is very simple. Let us do this job in ICCAT, not in CITES. This position is shared by the majority of Asian nations."

Afterward, Miyahara welcomed the decision but admitted the pressure would be on his country and others who depend on the Atlantic bluefin to abide by ICCAT. The organization ruled in November to reduce its quota from 22,000 tons to 13,500 tons for 2010. The body has also promised to rebuild the stock by 2022, which could include closing some fisheries if necessary.

"I feel more responsibly to work for the recovery of the species," Miyahara said. "So it's kind of a heavy decision for Japan too. The commitment is much heavier than before."

But many environmentalists have heard similar vows before, only to see them ignored and the tuna numbers plummet. A tuna ban was withdrawn at CITES in 1992 under the condition that fishing nations would improve their practices -- something they failed to do.

"The regional fisheries management organization in charge of this fishery has repeatedly failed to sustainably manage this fishery," said Sergi Tudela, head of fisheries at WWF Mediterranean. "ICCAT has so far failed miserably in this duty, so every pressure at the highest level must come to bear to ensure it does what it should."

Some environmentalists fear other marine proposals at the meeting could fail -- a worrisome trend given that the meeting had been billed as a chance to use international trade regulations to conserve ocean plants and animals.

A shark conservation proposal was defeated earlier this week and several other proposals to regulate the trade in endangered shark species are in trouble. The problem, many said, is that countries prefer to stick with regional organizations that often are controlled by powerful fishing interests and typically do all they can to protect fleets.

"We were expecting to have a real debate but it was not possible," said Gael de Rotalier of the European Union. "There was a strong feeling in the room against any involvement of CITES in marine issues. They were making it a matter of principle and not looking at the merits of the case."

The tuna defeat came hours after delegates rejected a U.S. proposal to ban the international sale of polar bear skins and parts, suggesting that economic interests at the meeting were trumping conservation.

The Americans argued that the sale of polar bears skins is compounding the loss of the animals' sea ice habitat due to climate change. There are projections that the bear's numbers, which are estimated at 20,000 to 25,000, could decline by two-thirds by 2050 due to habitat loss in the Arctic.

But Canada, Greenland and several indigenous communities argued the trade had little impact on the white bears' population and would adversely affect their economies.